At present, many electronic devices attain stale power supply from the conventional power supply device. When an electronic device is started up or hot-plugged, a very high surge appears, which may damage the elements of the electronic device or the power supply device. Many conventional technologies were developed to prevent the elements of the electronic device and the power supply device from being damaged by a surge, including: using the breaking of a switch element to block a surge, and using high voltage-withstand elements in the electronic device and the power supply device. A R.O.C. patent No. M250444 disclosed a “Surge-Inhibiting Power Source Protection Device”, which comprises: a surge inhibitor, a control circuit and a high voltage detection circuit. The high voltage detection circuit detects the voltage of power supply and sends a detection signal to the control circuit when there is an abnormal voltage. The detection signal makes the control circuit stop sending a trigger signal to the surge inhibitor. Once the surge inhibitor does not receive the trigger signal, the surge inhibitor interrupts the electrical connection between the power source and the electronic device. The abovementioned technology is only one of the conventional methods to protect electronic devices from surge. However, a power source may be connected to various loads in different occasions and generate surges of different voltage levels. Thus, the conventional protection circuits, which have only one check value to determine whether there is a surge in the output power, may cause incorrect operations and result in that the electronic device cannot be driven normally. Therefore, the conventional protection circuits still have room to improve.